In the fact-based film, Butler stars as Pennsylvania "hillbilly" Sam Childers, a violent, drug-fuelled criminal who, after finding God and reforming his home life, travels to the Sudan and builds an orphanage to protect young victims of slaughter and kidnapping from the Lord's Resistance Army.

When his humanitarian efforts are met with brutality, Childers doesn't so much turn the other cheek as pick up a grenade launcher. Put it this way: Machine Gun Preacher may be one of the few films that both fans of Rambo and The Blind Side can appreciate equally.

"He's one of the most interesting characters you could come across," Butler says in a downtown Toronto hotel.

"This is me growing up in a way. I think as you grow up you learn more and hopefully get better at your craft and take on more. This was a chance to be involved with a complex character who has so many things going on inside him -- as well as outside of him -- and try to encompass all of that.

"We had mammoth sessions of eight or nine hours in a day, where Jason, Marc and I really bonded and kept working to hone this script and make this story as powerful as possible ... I felt very involved in it. When I started shooting, I was already deeply plunged into his psyche."

A mindset that was darker than any he'd portrayed before, he adds.

"I've taken dark roles before -- 300 or Phantom of the Opera. I spent months making Phantom alone and depressed. As much as enjoyed it, I was in a lot of pain through that movie. But the Phantom didn't have to deal with children dying around him, fighting to save those children -- and losing."

After unspooling at the Toronto International Film Festival, Machine Gun Preacher opens across the country Sept. 30.